Monkey’s birthday party is interrupted by Barbequor (Robert Ridgely), an intergalactic villain who plans to eat the planets, and his sidekick, the Silver Spooner (Rob Paulsen).
Dee Dee dares Dexter into building her a giant robot similar to his Robo-Dexo 2000. They then team up to try to save an island’s population from being destroyed by an erupting volcano using their giant robots.
Dexter has a crush on his teenage babysitter Lisa (Kath Soucie). When he finds out that she has a boyfriend, he sabotages their relationship and accelerates his age by ten years in an attempt to win her heart.
Dexter thinks that a crazy homeless person balancing electronic devices on his head and muttering gibberish is a genius trying to contact aliens, so he takes him home.
When his mother falls ill, Dexter creates a robot to do her chores. Dee Dee gets hold of its remote control and wreaks havoc, forcing Dexter to create a second robot to counter Dee Dee’s.
Loading the player... During a trip to Japan as part of a student exchange program, Dexter accidentally releases a giant monster with an axe-like head from a volcano, forcing him to enlist the aid of his family to defeat it.
Dexter’s family goes to the beach, where Dexter tries to communicate with whales. He must rescue Dee Dee (dressed as a mermaid), when she is captured by manic pirates.
Dexter finds the exact opposite of his family, a hyperactive boy who is like Dee Dee and has scientist parents who are like Dexter. Sensing to fit in, he switches places with the boy.
To fix their apartment’s plumbing, Krunk and Valhallen go to the basement, where they meet Ratman (Maurice LaMarche), a diminutive vigilante raised by rats (a parody of Batman).
To learn more about girls, Dexter camouflages himself and enters Dee Dee’s room, where she is having a sleepover with her friends Lee Lee and Mee Mee. He gets caught by the girls, who force him to take part in their activities.
When Dee Dee frees one of Dexter’s robots by removing the wrench that froze it, the robot tries to destroy anyone who is mean to Dee Dee, including her friends, her mother and Dexter himself.
Dexter travels to the moon and finds that aliens are planning an invasion on Earth, and he uses his Robo-Dexo 2000 to stop them. It turns out that they only were interested in purchasing sweaters for the winter.
The U.S. army invades Dexter’s lab under the mistaken impression that aliens are using it as a base of operations on Earth, and Dexter must convince them that this is actually his lab, and also has to keep this a secret from Dee Dee.